Radiotherapy: Analysis of recurrances after radical treatment in Hodgkin's disease and possible additional chemotherapy. Participation in and supervision of proposed cooperative clinical trial of preoperative radiation in cancer of the rectocigmoid. Comparison of clinical material with mathematical models for fractionation in carcinoma of the skin. Sensitization of hypoxic tumor cells with neoarsphenamine in mice and possible preliminary pilot studies in patients. Physics: Development of computer systems for optimal treatment planning. Radiobiology: Investigations will include the physical and enzymological properties of phage T7 RNA polymerase; T7 gene mapping by RNA hydridization with T7 DNA and electron microscopy; the replication of DNA containing psoralen photo-cross-links; genetic analysis of E. coli temperature sensitive mutants blocking growth in cells carrying polA; the characterization of mutants for membrane synthesis and the relationship between cell membrane and DNA replication; the function in genetic recombination controlled by recA genes in E. coli; the mechanisms of DNA transfer and replication of F factors; the relation between vegetative DNA synthesis and that occurring during F factor transfer; post-replication DNA repair in bacteria and in mouse lymphoma cells; sensitization to X-rays of anoxic bacteria and mouse lymphoma cells by neoarsphenamine. Nuclear Medicine: The synthesis and testing of radionuclides with properties that may be suitable for diagnostic procedures.